This invention relates to solid state ballasts for gaseous discharge lamps, and more particularly to high frequency chopper ballasts without large magnetic and capacitive components that have additional energy storage circuitry to maintain lamp ionization during the valleys of the alternating current input voltage.
The common mercury lamp as well as other gaseous discharge lamps conventionally employ electromagnetic ballasts with bulky low frequency transformers and inductors and large power factor correction capacitors. A desirable high frequency chopper ballast that is highly efficient with low volume and light weight, with a good combination of features that an electronic ballast should have, is described in U.S. Pat. No. 3,890,537 granted on June 17, 1975 to John N. Park and Steven C. Peak jointly with the present inventor, and assigned to the assignee of this invention. This single phase, high frequency transistor chopper ballast operates on negligibly filtered full wave rectified line voltage and electronically shapes the line current by means of shaping the load current to obtain a high input power factor. Additionally, the d-c chopper ballast exhibits good regulation and starting current waveform, has low acoustic and radio frequency interference noise, eliminates acoustic resonance effects by sweeping the chopping frequency, and is stable over a usable temperature range.
The foregoing ballast circuit is especially suited for mercury vapor lamps, one feature being that during the valleys of the full wave rectified sinusoidal line voltage, minimum lamp current for good reignition characteristics in each cycle is maintained so that reignition occurs near the beginning of the cycle as the sinusoidal voltage rises. It will be evident that during the peaks of the 60 Hz wave sufficient voltage is available to operate the lamp normally, but as the rectified voltage falls toward zero there is not enough voltage available to keep the lamp running at its normal voltage and current. If the time during the valleys is longer than the deionization time of the lamp, the lamp may extinguish or considerable voltage may be needed for reignition on the subsequent rise of the 60 Hz wave. It is recognized that lamp deionization may be a complicated function of time but for simplicity of discussion the term "deionization time" is used here. For the mercury vapor lamp, the deionization time is sufficiently long that the lamp does not extinguish and reignition is obtained with the patented ballast at a relatively small voltage as the 60 Hz wave rises. Other gaseous discharge lamps such as the Lucalox (trademark of the General Electric Company) lamp, however, have a shorter deionization time than the mercury vapor lamp, perhaps as much as two to four times as fast. Accordingly, other techniques are needed to prevent such lamps from going out during the valleys of the sinusoidal energizing voltage and requiring a relatively high voltage to start up again.
A copending application by the inventor, Ser. No. 589,431, filed on June 23, 1975, entitled "Controlled Capacitive Filter for Active Loads", now U.S. Pat. No. 3,987,356, assigned to the same assignee, shows in FIG. 6 a ballast for a Lucalox lamp with a different type of filter. The present application relates to alternative arrangements with an auxiliary energy storage capacitor and control for use specifically as a lamp ballast.